Exhaust gas purification device for internal combustion engine

Abstract

A particulate filter ( 18 ) is arranged in the exhaust passage of an engine. Only the inner wall surface of downstream end open cells ( 61 d ) of the particulate filter ( 18 ) is covered with a NO x adsorbent ( 62 a ), and the inner wall surface of the upstream end open cells ( 61 u ) is covered with a HC adsorbent ( 63 a ). The particulates in the exhaust gas are trapped in the HC adsorbent ( 63 a ) or the cell walls ( 60 ) of the particulate filter ( 18 ) and prevented from reaching the NO x adsorbent ( 62 a ). When the catalyst temperature is low, NO x in the in flowing exhaust gas is adsorbed in the NO x adsorbent ( 62 a ), and hydrocarbon (HC) is adsorbed in the HC adsorbent ( 63 a ). With the increase in the catalyst temperature, the adsorbed NO x is desorbed from the NO x adsorbent ( 62 a ), and the adsorbed HC is desorbed from the HC adsorbent ( 63 a ). This HC reduces the NO x desorbed from the NO x adsorbent ( 62 a ).

What is claimed is:  
     
       1. An exhaust gas purification device for an internal combustion engine having an exhaust passage, comprising: 
       a filter arranged in said exhaust passage for trapping the particulates in the inflowing exhaust gas, said filter having an exhaust gas inflow surface and an exhaust gas outflow surface; and  
       a NO x  storing member arranged only on the exhaust gas outflow surface of the filter for temporarily storing NO x  in the inflowing exhaust gas therein.  
     
     
       2. An exhaust gas purification device according to  claim 1 , wherein said NO x  storing member is comprised of a NO x  adsorbent for adsorbing NO x  in the inflowing exhaust gas therein. 
     
     
       3. An exhaust gas purification device according to  claim 2 , further comprising NO x  desorbing means for desorbing NO x  adsorbed in the NO x  adsorbent therefrom by heating said NO x  adsorbent. 
     
     
       4. An exhaust gas purification device according to  claim 3 , wherein said NO x  desorbing means comprises secondary air supply means for supplying a secondary air to the NO x  adsorbent when said NO x  is to be desorbed from said NO x  adsorbent, and means for heating said secondary air, said NO x  adsorbent being heated by causing the heated secondary air to flow through said NO x  adsorbent. 
     
     
       5. An exhaust gas purification device according to  claim 4 , wherein said secondary air supply means supplies the secondary air to the filter in such a manner that the secondary air flows from the exhaust gas outflow surface of said filter toward the exhaust gas inflow surface of said filter, and NO x  desorbed from said NO x  adsorbent is reduced by reacting with the particulates trapped in said filter. 
     
     
       6. An exhaust gas purification device according to  claim 5 , wherein said NO x  desorbing means comprises means for preventing the exhaust gas discharged from the engine from flowing into said filter when said NO x  desorbing means desorbs NO x  from said NO x  adsorbent, and said NO x  desorbing means desorbs NO x  from said NO x  adsorbent when the engine load is lower than a preset load. 
     
     
       7. An exhaust gas purification device according to  claim 3 , further comprising reducing agent supplying means for supplying a reducing agent to said NO x  adsorbent when NO x  is desorbed from said NO x  adsorbent, wherein NO x  is reduced by said reducing agent. 
     
     
       8. An exhaust gas purification device according to  claim 7 , wherein said reducing agent supplying means comprises a HC adsorbent arranged on the exhaust gas inflow surface of said filter or on the exhaust gas outflow surface of the filter with said NO x  adsorbent being deposited thereon for adsorbing the hydrocarbon in the inflowing exhaust gas, and the hydrocarbon adsorbed in said HC adsorbent is desorbed therefrom to be supplied to said NO x  adsorbent when NO x  is desorbed from said NO x  adsorbent. 
     
     
       9. An exhaust gas purification device according to  claim 8 , wherein said reducing agent supplying means comprises a fuel injector for injecting fuel directly into a cylinder, and hydrocarbon is supplied to said HC adsorbent by injecting a secondary fuel from said fuel injector when the engine is in an expansion stroke or in an exhaust stroke. 
     
     
       10. An exhaust gas purification device according to  claim 3 , further comprising means for increasing the temperature of the exhaust gas flowing into said NO x  adsorbent when desorbing NO x  from said NO x  adsorbent, wherein said NO x  adsorbent is heated by causing said exhaust gas to flow through said NO x  adsorbent. 
     
     
       11. An exhaust gas purification device according to  claim 2 , wherein said NO x  adsorbent is composed of at least one selected from: a precious metal including palladium, platinum and rhodium; a transition metal including copper and iron; and lithium. 
     
     
       12. An exhaust gas purification device according to  claim 1 , wherein said NO x  storing member is comprised of a NO x  absorbent for absorbing NO x  therein when the air-fuel ratio of the inflowing exhaust gas is lean and releasing and reducing the absorbed NO x  when the oxygen concentration in the inflowing exhaust gas becomes lower. 
     
     
       13. An exhaust gas purification device according to  claim 12 , further comprising NO x  releasing means for releasing NO x  from said NO x  absorbent by temporarily making the air-fuel ratio of the exhaust gas flowing into said NO x  absorbent rich. 
     
     
       14. An exhaust gas purification device according to  claim 13 , further comprising a SO x  absorbent arranged on the exhaust gas inflow surface of said filter or on the exhaust gas outflow surface of the filter with said NO x  absorbent being deposited thereon, said SO x  absorbent absorbing SO x  in the inflowing exhaust gas therein when the air-fuel ratio of the inflowing exhaust gas is lean, and releasing the absorbed SO x  therefrom when the oxygen concentration in the inflowing exhaust gas becomes lower while the temperature of the SO x  absorbent is higher than a SO x  release temperature, wherein the temperature of the SO x  absorbent is prevented from being higher than said SO x  release temperature when NO x  is released from said NO x  absorbent. 
     
     
       15. An exhaust gas purification device according to  claim 13 , wherein said NO x  releasing means comprises a fuel injector for injecting fuel directly into a cylinder, and the air-fuel ratio of the exhaust gas flowing into said NO x  absorbent is made rich by injecting a secondary fuel from said fuel injector when the engine is in an expansion stroke or in an exhaust stroke. 
     
     
       16. An exhaust gas purification device according to  claim 12 , wherein said NO x  absorbent is comprised of: at least one selected from an alkali metal including potassium, sodium, lithium and cesium, an alkali earth metal including barium and calcium and a rare earth metal including lanthanum and yttrium; and a precious metal including palladium, platinum and rhodium. 
     
     
       17. An exhaust gas purification device according to  claim 1 , further comprising means for estimating the amount of NO x  absorbed in said NO x  storing member, wherein NO x  stored in said NO x  storing member is released when said estimated amount of NO x  is larger than a preset NO x  amount. 
     
     
       18. An exhaust gas purification device according to  claim 1 , further comprising poisoning material removing means arranged on the exhaust gas inflow surface of the filter or on the exhaust gas outflow surface of the filter with said NO x  storing member being deposited thereon for preventing a poisoning material from reaching said NO x  storing member. 
     
     
       19. An exhaust gas purification device according to  claim 18 , wherein said poisoning material removing member is comprised of a HC adsorbent for adsorbing hydrocarbon in the inflowing exhaust gas therein. 
     
     
       20. An exhaust gas purification device according to  claim 19 , wherein the stored NO x  is released from said NO x  storing member and caused to react with hydrocarbon when said hydrocarbon is desorbed from said HC adsorbent. 
     
     
       21. An exhaust gas purification device according to  claim 19 , wherein said HC adsorbent is comprised of at least one selected from a precious metal including platinum and palladium and a transition metal including copper and iron, carried on a carrier composed of zeolite. 
     
     
       22. An exhaust gas purification device according to  claim 18 , wherein said poisoning material removing member is comprised of a SO x  absorbent, said SO x  absorbent absorbing SO x  in the inflowing exhaust gas therein when the air-fuel ratio of the inflowing exhaust gas is lean, and desorbing the absorbed SO x  therefrom when the oxygen concentration in the influent exhaust gas becomes lower while the temperature of the SO x  absorbent is higher than a SO x  release temperature. 
     
     
       23. An exhaust gas purification device according to  claim 22 , wherein said filter is regenerated immediately after SO x  is released from said SO x  absorbent. 
     
     
       24. An exhaust gas purification device according to  claim 22 , wherein the temperature of the SO x  absorbent is increased by increasing the temperature of the exhaust gas flowing into the SO x  absorbent when SO x  is released from said SO x  absorbent. 
     
     
       25. An exhaust gas purification device according to  claim 24 , further comprising a fuel injector for injecting fuel directly into a cylinder, wherein the temperature of the exhaust gas flowing into said SO x  absorbent is increased by injecting a secondary fuel from said fuel injector and burning the secondary fuel when the engine is in expansion stroke or in exhaust stroke. 
     
     
       26. An exhaust gas purification device according to  claim 22 , wherein said SO x  absorbent is comprised of at least one selected from: a transition metal including iron, manganese, nickel and tin; and lithium. 
     
     
       27. An exhaust gas purification device according to  claim 18 , further comprising means for estimating the amount of the poisoning material stored in said poisoning material removing member and means for releasing the poisoning material from said poisoning material removing member when the estimated amount of said poisoning material is larger than a preset poisoning material amount. 
     
     
       28. An exhaust gas purification device according to  claim 18 , wherein the NO x  releasing from said NO x  storing member, the releasing of the poisoning material from said poisoning material removing member, and the regeneration of said filter are performed at the same time. 
     
     
       29. An exhaust gas purification device according to  claim 1 , further comprising filter regenerating means for burning the particulates by heating said filter while placing the filter in an oxidazing atmosphere to regenerate said filter. 
     
     
       30. An exhaust gas purification device according to  claim 29 , further comprising trapped particulate amount estimation means for estimating the amount of the particulates trapped in said filter, wherein said filter regenerating means regenerates said filter when the estimated amount of the particulates trapped in said filter is larger than a preset particulate amount. 
     
     
       31. An exhaust gas purification device according to  claim 29 , wherein the NO x  releasing from said NO x  storing member and the regeneration of said filter are performed at the same time. 
     
     
       32. An exhaust gas purification device according to  claim 1 , wherein said filter comprises a plurality of cells defined by a porous cell wall extending substantially in parallel to an axis of the exhaust passage, said cells including upstream end open cells with an exhaust upstream ends thereof being opened and exhaust downstream ends thereof being closed, and downstream end open cells with exhaust upstream ends thereof being closed and exhaust downstream ends thereof being opened, said upstream end open cells and said downstream end open cells being arranged alternately in repetitive fashion, and wherein said NO x  storing member is arranged only on inner wall surfaces of said downstream end open cells. 
     
     
       33. An exhaust gas purification device for an internal combustion engine having an exhaust passage, comprising: 
       a filter arranged in said exhaust passage for trapping the particulates in the inflowing exhaust gas;  
       a NO x  storing member arranged in said exhaust passage downstream of said filter for temporarily storing NO x  in the inflowing exhaust gas therein;  
       estimating means for estimating an amount of NO x  stored in said NO x  storing member; and  
       regeneration/release means for regenerating said filter and releasing the accumulated NO x  from said NO x  storing member, in an oxidation atmosphere, when said estimated accumulated NO x  amount is larger than a preset NO x  amount, wherein said regeneration/release means releases the accumulated NOx from said NOx storing member when said filter is to be regenerated.  
     
     
       34. An exhaust gas purification device according to  claim 33 , wherein said NO x  storing member is comprised of a NO x  adsorbent for adsorbing NO x  in the inflowing exhaust gas. 
     
     
       35. An exhaust gas purification device according to  claim 34 , wherein said regeneration/release means comprises heating means for heating said filter in an oxidation atmosphere and heating said NO x  adsorbent when said filter is to be regenerated and NO x  is to be desorbed from said NO x  adsorbent. 
     
     
       36. An exhaust gas purification device according to  claim 34 , wherein said NO x  adsorbent is comprised of at least one selected from: a precious metal including palladium, platinum and rhodium, a transition metal including copper and iron; and lithium. 
     
     
       37. An exhaust gas purification device according to  claim 33 , wherein said NO x  storing member is comprised of a NO x  absorbent for absorbing NO x  therein when the air-fuel ratio of the inflowing exhaust gas is lean, and releasing the absorbed NO x  therefrom when the oxygen concentration of the inflowing exhaust gas becomes lower. 
     
     
       38. An exhaust gas purification device according to  claim 37 , further comprising air-fuel ratio control means for heating the filter in an oxidation atmosphere and temporarily make the air-fuel ratio of the exhaust gas flowing into said NO x  absorbent rich, when said filter is to be regenerated and NO x  is to be released from said NO x  adsorbent. 
     
     
       39. An exhaust gas purification device according to  claim 37 , wherein said NO x  absorbent is comprised of: at least one selected from an alkali metal including potassium, sodium, lithium and cesium, an alkali earth metal including barium and calcium, and a rare earth metal including lanthanum and yttrium; and a precious metal including palladium, platinum and rhodium. 
     
     
       40. An exhaust gas purification device according to  claim 33 , wherein said filter has an exhaust gas inflow surface and an exhaust gas outflow surface, and said NO x  storing member is arranged on the exhaust gas outflow surface of said filter.